Experimental and Theoretical Studies of Oxygen Gradients in Rat Pial Microvessels

Abstract

Using modified oxygen needle microelectrodes and intravital videomicroscopy, measurements were made of tissue oxygen tension (PO₂) profiles near cortical arterioles and transmural PO₂ gradients in the pial arterioles of the rat. Under control conditions, the transmural PO₂ gradient averaged 1.17 ± 0.06 mm Hg/μm (mean ± s.e., n = 40). Local arteriolar dilation resulted in a marked decrease in the transmural PO₂ gradient to 0.68 ± 0.04 mm Hg/μm ( P < 0.001, n = 38). The major finding of this study is a dependence of the transmural PO₂ gradient on the vascular tone of the pial arterioles. Using a model of oxygen transport in an arteriole and experimental PO₂ profiles, values of radial perivascular and intravascular O₂ fluxes were estimated. Our theoretical estimates show that oxygen flux values at the outer surface of the arteriolar wall are approximately 10⁻⁵mL O₂/cm² per sec, independent of the values of the arteriolar wall O₂ consumption within a wide range of consumption values. This also means that PO₂ transmural gradients for cerebral arterioles are within the limits of 1 to 2 mm Hg/μm. The data lead to the conclusion that O₂ consumption of the arteriolar wall is within the range for the surrounding tissue and O₂ consumption of the endothelial layer appears to have no substantial impact on the transmural PO₂ gradient.